1. Field of the Invention
The present invention relates to a piezoelectric actuator utilizing an electrostrictive lengthwise effect which is suitable for use in piezoelectric actuators.
2. Description of the Prior Art
A piezoelectric actuator is designed to obtain a minute mechanical displacement utilizing a piezoelectric actuator (hereinafter referred to as "actuator") which can convert electric energy into mechanical energy and is used in the field of applications which require precise control of movement of a minute position, such as a mass flow controller used in manufacturing apparatus of semiconductor IC circuits, an X-Y table used in exposure systems for the manufacture of the IC circuits, plastics injection molding machines and so on.
One of such a type of conventional piezoelectric actuators is described in Japanese Journal of Applied Physics, Vol. 24 (1985), Supplement 24-3, pp. 209-212.
As shown in FIG. 1, the prior art piezoelectric actuator comprises a laminated sintered member including a plurality of piezoelectric active layers (hereinafter referred to as "active layer") 2a, 2b, 2c, 2d . . . 2k, 2l and 2m, each layer being made of an electrostrictive ceramic material, a plurality of internal electrodes 1a, 1b, 1c . . . 1m and 1n made of silver, palladium alloy or platinum, each of which is placed between each pair of piezoelectric active layers, and inactive layers 3a and 3b each in the form of thicker electrostrictive ceramic sheet, these inactive layers 3a and 3b being located to cover the opposite ends of the laminated sintered member. The laminated sintered member also comprises insulating layers 4a, 4b, 4c . . . 4m and 4n of glass or the like disposed to insulate the internal electrodes 1a, 1b . . . 1n on alternate layers; a pair of external electrodes 5a and 5b disposed at opposite sides of the laminated sintered member and disposed to perform electric connection on alternate internal electrodes; and a pair of leads 6a and 6b electrically connected with the external electrodes 5a and 5b, respectively.
In such an arrangement, the piezoelectric active layer assembly 2 is expanded in its longitudinal direction and contracted in a direction perpendicular to said longitudinal direction when an electric field is applied to the piezoelectric actuator. On the other hand, the inactive layers 3a and 3b are not subject to any piezoelectric effect. As a result, the piezoelectric active layer assembly 2 is brought into intense engagement with the inactive layers 3a and 3b. Since the piezoelectric active layer assembly 2 is incorporated integrally between the inactive layers 3a and 3b, the piezoelectric actuator is deformed without slippage at the interface between each pair of adjacent layers. As a result, the opposite end faces of the piezoelectric actuator will be bulged outwardly, as shown in FIG. 2.
This will create uneven strain in the piezoelectric actuator.
The uneven strain may be overcome if the opposite end faces of the piezoelectric actuator are adhered to any smooth fixed surfaces. However, this may cause internal stress in the piezoelectric actuator and, in the worst case, may break the element.